Crevalle said:There are some minerals included in aquarium salt (coralife, instant ocean, etc), but it still isn't equivalent to sea water. In other words, it does not replace the essential elements in the ocean's water. It matters in a reef tank because the more you top-off, the more you are stripping the water, rather than replacing minerals, despite at a slow rate.
Doesn't the mineral content of spring water vary greatly, depending on the source? Couldn't you have too much of some minerals by using spring water?